You can see what the typical stipend was for teaching assistants and research assistants for last year's admitted students at http://www.gradschoolshopper.com
, just search for a school, look at the .pdf document and scroll to the second page. It can be as high as $25,000 to even $35,000 at Stanford, but more typically stipends are between $15,000 and $20,000 per year. Enough to support yourself, but not really enough to support a family. They do not give you more money if you are married, your wife would have to apply and get accepted individually.